Top end tear down - not looking good...

So, I tore down my top end tonight on my 2006 YZ250F. My cams looked good, but then I removed the cylinder, and had scoring and a burn mark on the back side of the piston, and scoring on in the cylinder. e

Also, where the connecting rod connects to the crank, there is some "blueing". You will see that in the pics below. What does that mean?

Side note, when I took the cams out, I checked the valve clearance. On hte intake valves, I couldn't even get a .05 mm feeler to fit. The exhaust valves seemed fine.

I'm wondering what my options are? Do I need a new cylinder? Here's some pics:

IMG_7018.jpg

IMG_7021.jpg

I'm looking for advice...Am I just screwed on this? If I can find a cylinder, do I need to do anything to the bottom end?

Thanks.

That part of the crank is really not used in the process of engine operation so if there is no marks or scoring where the rod connects to the crank I wouldn't worry about it and was probably caused by the manufacturing process. Was there oil in the bike? Was there oil pressure? How many hours are on the engine?

Thanks for the reply.

I'm the guy who might win "bonehead of the year" award. Last weekend I was on my first ride of the year. I had just changed my oil. On the 3rd lap around the track (easy laps), my engine stalled. I restarted it, drove it 50 yards, and it stalled again. I got off and noticed oil dripping from the skid plate. I pushed it back to the trailer, took off the skid plate, and noticed the little oil tank drain plug was missing. I must have only finger tightened that plug (I was chasing my 3 year old while I was changing the oil). I took the bike home, put a drain plug in it, and it's been running since. It starts on the first or second kick.

There were low hours on this engine.

Do I have any options other than new cylinder or replating / resleeving?

What do you guys think about the intake valves being so tight? Should I just order a shim kit?

Thanks.

It definitely looks like you squeaked the piston with no oil. There is a very small chance the cylinder is salvageable. You can get some muriatic acid and dab some on the score marks and let it sit for a moment, then try to wipe them. There is a chance that the marks on the cylinder are melted aluminum from the piston that is smeared on the nikasil of the cylinder. If so then the acid will melt the aluminum and leave the nikasil unharmed. Chances are though that the cylinder is scored and needs to be replated or replaced. Since it costs more to get it replated than to just buy a new cylinder, I would just buy a new one if your cylinder is no good.

The bluing on the crank is nothing to worry about, it is from the manufacturing process.

As for the valves, you have worn through the ti-nitride coating on the valve faces and they have started to tighten up. If you shim them into spec now they will last a couple rides and tighten up again. At this point they will need to be replaced. Since the engine is apart now, it is probably easier to replace them now than to pull the head off again in a few rides and replace them. Make sure to get the seats cut by a professional before you put in the new valves.

It definitely looks like you squeaked the piston with no oil. There is a very small chance the cylinder is salvageable. You can get some muriatic acid and dab some on the score marks and let it sit for a moment, then try to wipe them. There is a chance that the marks on the cylinder are melted aluminum from the piston that is smeared on the nikasil of the cylinder. If so then the acid will melt the aluminum and leave the nikasil unharmed. Chances are though that the cylinder is scored and needs to be replated or replaced. Since it costs more to get it replated than to just buy a new cylinder, I would just buy a new one if your cylinder is no good.

The bluing on the crank is nothing to worry about, it is from the manufacturing process.

As for the valves, you have worn through the ti-nitride coating on the valve faces and they have started to tighten up. If you shim them into spec now they will last a couple rides and tighten up again. At this point they will need to be replaced. Since the engine is apart now, it is probably easier to replace them now than to pull the head off again in a few rides and replace them. Make sure to get the seats cut by a professional before you put in the new valves.

Do you need to provide the new valve train to the seat cutter? Who typically cuts seats? Thanks!

Do you need to provide the new valve train to the seat cutter? Who typically cuts seats? Thanks!

You don't need to provide the new valves for them to cut it if they are using a Serdi machine or Newen CNC cutter. These are the two best methods of cutting seats, so I suggest you find a place that can do one of these. I know MX-time inc. is a popular choice, as is Ron Hamp.

Also, make sure that you do not lap the valves if you stay with titanium valves, just get the seats cut and drop them in. Lapping titanium valves can damage them and cause them to wear out prematurely.

I've worked in the same place for close to 14 years, and didn't even realize that I have a company a block away that just does motorsports cylinders...specifically MX and ATV cylinders. The company name is Max Power RPM's. Apparently they have a long history of doing cylinders for the pro's (James Stewart, etc.).

I stopped by this morning and had them take a look at my cylinder. They said they may be able to hone it ($50). If that doesn't work, they can replate it for $175. Their website is www.maxrpms.net

2 questions...First, it looks like I can get a new OEM cylinder for about $200. Which is better, replating or going with the new cylinder?

Second, is it ok to hone these cylinders? I thought you couldn't do that with this type of cylinder? Obviously these guys know what they are doing...That's mostly what they do is cylinders.

Thanks!

if its only 25$ more, i would just get the new cylinder and call it good

I was told the aftermarket coating like Maxpowers is much better than stock.

I have an 07 WR250 that I had replated for a bog bore kit that I did in 07 that stills looks perfect. Been riidng the schitt out of it every weekend.

Here's an update on the tight valves...

I've talked with 2 different people who told me to pour liquid into the intake port and see if anything leaks out the valves. I filled up the port, let it sit for about a minute. There wasn't a single drop that leaked out the valves.

Does this mean that the valves are alright, and that they were just tight?

What should I do from here?

Thanks!

Aftermarket plating is much better than stock new plating, Most likely Max RPM sends their stuff to Millennium Technologies in Plymouth WI.

Like KJ790 said, your valves are worn past the hard coating. Once the hard coating is worn you are relying on the soft Titanium. It is highly recommended that you get the seats cut, and new factory Ti valves/springs/seals installed before you drop a valve.

I don't doubt that the valves are sealing fine, that was never the issue at all. If the valve clearance is tight then that means that they have worn into the seats. Titanium is not an ideal metal for a valve, so they put a very thin, but very tough coating on the face of titanium valves to make them hold up. This coating prevents the valves from wearing for a long time, and thus the clearance remains in spec for a long time. Once the coating wears out the valve itself beings to wear, and at a fast rate. This is when the valve becomes tight. The first time the valve tightens up you can change the shim and get it back into spec and be safe. However, you are now running on a valve with no hard coating left, which means in a few hours of run time the valve will have worn to the point of being too tight again. At this point the face of the valve is getting pretty thin. You can shim it back into spec again, but now you are dealing with a time bomb and it could break and destroy your whole motor. My rule of thumb is shim a valve once, the next time it is tight the valve gets replaced.

This brings us to your situation. Your valves are tight right now, so you could shim them and get a couple more hours out of them. However, the head is off right now, so it would be easy to replace them now. If you don't mind pulling the head back off and spending another $30 on a head gasket then you can shim them for now and then pull the head off in 10-20 hours when the valves tighten back up and replace the valves then. It's your call, but most people would just replace them while the head is off now to save the work in the near future.

So when I got home tonight, I pulled one of the buckets from the head, and looked at the shim in the bucket. The shim in the bucket was a 185. I thought I read in the service manual that the stock shim was a 175?

If the stock shim is a 175 but there are 185's installed, wouldn't that contribute to my tight valve situation?

Thanks.

There is no such thing as a stock shim, they come in all different sizes from the factory. This is due to machining tolerances, every part of an engine is made with a tolerance, so each part is slightly different, so it takes different sized shims to get the correct clearance. Typically these bikes come with shims ranging from 170-190 from the factory. Since yours is a 185 that says to me that the valve has never been shimmed before and that is most likely the original shim from the factory.

My rule of thumb is shim a valve once, the next time it is tight the valve gets replaced.

How much longer is the seat life of the valves extended, if one replaces the valves as early as you suggest on a brand new head?

How much longer is the seat life of the valves extended, if one replaces the valves as early as you suggest on a brand new head?

I'm not sure what you are asking. Are you asking how many times you can cut the seats for new valves before they need to be replaced? That depends on how deep the seat is cut each time, but if they are cut by someone who knows what he is doing you can cut seats a a few times (3-4 times) before the seat needs to be replaced.

I'm not sure what you are asking. Are you asking how many times you can cut the seats for new valves before they need to be replaced? That depends on how deep the seat is cut each time, but if they are cut by someone who knows what he is doing you can cut seats a a few times (3-4 times) before the seat needs to be replaced.

No, I was not asking how many times they can be cut, I was trying to ask this:

Will replacing the valves as early as you suggest, extend the overall life of the seats in a brand new head? - I know they still have to be cut for the next set of valves, but I was wondering if the new valves slow down eating away at the newly cut seat. I was wondering if the seats are softer after they are cut, meaning I thought maybe the seats had a specialized coating on them as well before they are cut the first time.

Edited by nokickstandsallowed
Clarification.
No, I was not asking how many times they can be cut, I was trying to ask this:

Will replacing the valves as early as you suggest, extend the overall life of the seats in a brand new head? - I know they still have to be cut for the next set of valves, but I was wondering if the new valves slow down eating away at the newly cut seat. I was wondering if the seats are softer after they are cut, meaning I thought maybe the seats had a specialized coating on them as well before they are cut the first time.

Oh, gotcha. No coating on the seats. As long as the face of the seat matches the face of the valve (i.e. the seat was originally cut correctly and then wore with the valve) then seat wear will be pretty consistent.

Oh, gotcha. No coating on the seats. As long as the face of the seat matches the face of the valve (i.e. the seat was originally cut correctly and then wore with the valve) then seat wear will be pretty consistent.

Could you give a rough estimate as to how much money valve maintenance is a year going with the principle of changing them out after shimming just once and having the seats cut say putting 30 hours a month on the meter? I did the calculations, and at this point, it is a tough decision between buying valves that quickly with seat cutting each time versus just buying the head at $390 and adding $240 in valves. Getting the seats cut at say $80 to $100 for all five plus $240 in valves each time is a tough call depending on how many times a year that is being done. How many times a year do you get the seats cut if your riding 30 hours a month?

Edited by nokickstandsallowed
Accuracy correction.
Could you give a rough estimate as to how much money valve maintenance is a year going with the principal of changing them out after shimming just once and having the seats cut say putting 30 hours a month on the meter? I did the calculations, and at this point, it is a tough decision between buying valves that quickly with seat cutting each time versus just buying the head at $390 and adding $240 in valves. Getting the seats cut at say $80 to $100 for all five plus $240 in valves each time is a tough call depending on how many times a year that is being done. How many times a year do you get the seats cut if your riding 30 hours a month?

Why would you ever buy a new head when there is nothing wrong with your old head? At those prices getting the seats cut would save you $290 each time the valves wore out. It's hard to estimate how long the valves will last, that depends on your air filter maintenance and how you ride. With good filter maintenance and hard MX riding these bikes tend to go 150+ hours before they need valves. However if you are doing 30 hours a month then odds are you are not doing hard MX racing, most likely trail riding and tight single track, which is much easier on valves. When the bike is not being revved high much these valves have been known to last 300+ hours. I've never heard of anyone who wasn't a pro needing to replace their valves multiple times a year unless they let dirt get past the air filter.

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